CD1865 Datasheet, PDF (64/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

CD1865 — Intelligent Eight-Channel Communications Controller
Because the CD1865 performs flow-control functions before the data is passed to the host, the
response time required of the host to avoid data overrun is greatly reduced. Additionally, the flow-
control characters can be stripped from the data stream, relieving the host from processing them.
To use automatic flow-control, the Special Character Detection (SCDE) must be enabled by bit 4 of
Channel Option register 3 (COR3). This causes all error-free received data to be compared for a
match with the Special Character registers (SCHR1–4). In addition, flow-control must be enabled
by Transmit In-Band Enable (TxIBE, bit 6) of COR2. This causes the special characters to be
interpreted as flow-control characters. For single-character flow-control sequences, SCHR1 is used
as Xon and SCHR2 as Xoff. SCHR3–4 are available for use as normal special-detect characters. If
two-character sequences are enabled by XoffCH and XonCH (bits 6 and 7) of COR3, SCHR1 and
SCHR3 form the Xon sequence, and SCHR2 and SCHR4 form the Xoff sequence.
If flow-control characters are passed to the host, they are marked as special characters 1 or 2 in the
Receive Channel Status register (RCSR). If a two-character sequence is detected, it is compressed
to the second character and a status indicating a match of the first character is set. A valid two-
character sequence requires that both characters be received without error; if an error occurs on the
second character the first character is treated as a normal character, and this does not affect non-
flow control special character detection.
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Datasheet